でも、本当に存在しないやつとはエラーが違うのでなにかありそう

$ swiftc -emit-ir -Xcc --target=wasm32aaa first.swift -o first.ll <unknown>:0: warning: argument unused during compilation: '-mmacosx-version-min=10.9.0' <unknown>:0: error: -fobjc-arc is not supported on platforms using the legacy runtime <unknown>:0: error: unknown target triple 'wasm32aaa', please use -triple or -arch <unknown>:0: error: clang importer creation failed